Matter and energy are related; one can convert into the other. What is it called when this happens?

For example, solids melt/liquefy into liquid, and liquid vaporizes into gas. Gas condenses into liquid, and liquid solidifies into solid.

So matter [verb] into energy, and energy [verb] into matter. What are the correct verbs to use here? I am thinking that they are "energize" and "materialize", but I'm not sure, especially about "energize".

4 Answers
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Annihilation is the word you must be looking for. When a low-energy electron annihilates a low-energy positron (antielectron), two or more $\gamma$-ray photons are produced, the process is called annihilation$_1$. If a $\gamma$-ray photon materializes into an electron and positron pair, the process is called pair-production.$_2$

Probably you must have got one verb "materialize" but you haven't got the verb for vice versa process.

So you are saying that the terms are not particularly set, but that materialize and dematerialize are common and probably the best ones to use? Annihilation, as I understand it, is specifically when a particle collides with its antiparticle. Is this the only way that we know that matter converts to energy? If not, then annihilation is a kind of "dematerialization".
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fredsbendJun 4 '14 at 3:55

"In fact, everything we know is only some kind of approximation, because we know that we do not know all the laws as yet. Therefore, things must be learned only to be unlearned again or, more likely, to be corrected."-Feynman. Now, you should have understood, why I say "probably" always. As I understand now, as a layman, annihilation is a kind of "dematerialization". I will be happy to hear form others, if it is wrong. I will try to find other ways in which annihilation takes place.
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FeynmanJun 4 '14 at 4:30

Coming back again a few months later, I find this answer interesting. It perhaps illuminates a fundamental problem with the question. Can you expand on this a bit? What are the types of energy and why is conversion between them different than matter converting between states? Being that scientists like having special terms for most things, I'm surprised that conversion from one specific form of energy to another specific form does not have a name beyond the generic "convert". Here's a +1 in advance.
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fredsbendNov 15 '14 at 8:18

Matter and energy are related; one can convert into the other. What is it called when this happens?

Matter in the sense of "mass" is related to energy through the famous E=m*c**2 of Special Relativity. That is the only framework where conversion of matter to energy has a meaning in physics.

Your example:

For example, solids melt/liquefy into liquid, and liquid vaporizes into gas. Gas condenses into liquid, and liquid solidifies into solid.

is out of classical physics, thermodynamics, and it is talking of phase transitions of matter. There is no change of matter to energy or energy to matter in your example. There is only a change in the form of energy, from kinetic to potential, binding the individual atoms and molecules dependent on the temperature . So solids turn into liquids and liquids to gas depending on temperature. "turn" is a better turn of language :) to "transition" which is the physics term.

Then again you go into a phrasing that is appropriate for special relativity:

So matter [verb] into energy, and energy [verb] into matter.

Here you can use "converts" if you are discussing fusion and fission reactions, mass converts to energy, also "becomes" and "turns" are not wrong turns of phrase. If an energetic photon creates an electron positron pair in the field of an atom or nucleus, "the energy of the photon partially converts to matter" is fine ( a lot of the incoming energy goes to kinetic energy, momentum balances, and a scattered photon of less energy).

What are the correct verbs to use here? I am thinking that they are "energize" and "materialize", but I'm not sure, especially about "energize".

It is not conversion rather an equivalence. If a closed box at rest contains an amount of energy of E then the mass (defined as the inertia of the box) will be E/c^2. It doesn't matter if that energy is simply a solid ball of iron or if it is thermal radiation.